1. Field of the Invention
This invention relates to mast assemblies in general, and more particularly, to a non-traditional or unconventional mast assembly where an additional boom member is provided along the upper edge of the sail to increase the sail surface area, reduce sail top deflection and allow for independent control of the sail base and top.
2. Preliminary Discussion
Mankind has for centuries had a devotion to the art of sailing. Since the dawn of recorded history, humans have been utilizing the power of the wind to propel water borne and even ocean-going vessels. The first boats were configured with pocket-like sails which caught the wind flowing from behind the boat and propelled the boat in the general direction of the wind. One of the primary focuses of modern nautical engineering has been toward sail designs that allow the boat to travel closer to the wind, i.e. with a lesser angle between the boat and wind directions. Most modern boats can sail within 35.degree. of the wind direction under average conditions. However, since the days of Julius Caesar, it is estimated this figure has only dropped by 15.degree. from a minimum angle of 50.degree. to the wind. The reason is that as the angle to the wind decreases, the turbulence generated by a conventional vertical mast increases and the sail stalls, or in aerodynamic terms does not produce "lift." Nevertheless, the race to design a boat capable of sailing farther into the wind still continues. One of the principal reasons sailing is pleasant is that "you can sail your trusty boat in any direction, regardless of where the ornery wind happens to be blowing."
A second drawback to the conventional vertical mast is the lack of control of the sail top. A "boom," positioned at the lower end of the sail, or along the sail base, controls the general angle of attack of the sail by regulating the position of the sail base. However, without a top boom or similar positioning device of some sort, the sail top deflects independently of the bottom boom. Such deflection is a function of the sail material, wind speed and wind direction. Consequently, the sail does not maintain the most efficient or desirable angle of attack along its length. A so-called Marconi or triangular sail alleviates this problem to a considerable extent by simply omitting sail material or essentially half the sail with tension on the sail so the outer edge is stretched and stiffened. Gaff rigged sails have been frequently used both on so-called fore and aft rigs and also, of course, on so-called square sail rigs. Gaff rigs are difficult to control, however, particularly in so-called fore and aft rigs and the use of the gaff-type rig has declined in favor of the Marconi rigs. The gaff rig, in any event, was designed primarily to prevent the sail from losing its shape and support a large sail on a short mast, not to control the top angle of attack of the sail to the wind.
A conventional sail, which is really just a thin flexible member, translates the fluid motion of the wind into propulsive power by capturing the wind in the "pocket" of the sail such that the sail forms a foil-like shape similar to that of an airplane wing. This wing shape is such that the difference in curvature creates a pressure difference across the wing or sail, thereby generating "lift" and "drag" forces on the sail. These sail forces result in a net force on the boat transferred through the mast. The component of the net boat force in the direction of travel is the "propulsive" force and the complimentary force, perpendicular to the direction of travel, is the heeling force. If the propulsive force exceeds the net drag forces on the boat, forward motion is achieved.
A conventional vertical mast-sail system has one serious flaw. Because the surface of the mast facing the wind is hundreds of times larger than the thickness of the sail, the air leaving the mast's trailing edge is turbulent, thereby creating a large turbulent wind "shadow" along the sail's leading edge. Since the largest "lift" force occurs at the sail's leading edge, the turbulent wind shadow caused by the mast destroys much of the sail's "lift" or drive potential transverse to the direction of the wind. To correct for this inefficient leading edge, boat manufacturers reduce the main sail area and overcompensate with a large front sail, or "jib." The jib has a so-called "wire" leading edge that is approximately 20 times thicker than the thickness of the main sail compared to the mast which may be in approximate terms hundreds of times thicker. As a result, the wire produces a smaller, negligible turbulent wind shadow, thereby utilizing the full leading edge lift or drive force.
However, there are problems associated with using a large jib and a small main sail. Because the jib produces the majority of the propulsive force, a net force moment results about the center of the boat and the captain must compensate with the rudder in order to maintain a straight course. The result is increased drag from the rudder or rudders. However, as inefficient as this method is, it surpasses the traditional large main sail configuration and has been adopted by most nautical engineers in high performance boats.
Even with the advent of the powerboat, the constant research and improvements in sailing design have not ceased, with the major areas of focus being on sailing speed and sailing direction, each a function of "lift" or drive generated by the sail and sail efficiency respectively. There is always a need, therefore, to improve upon existing designs in an effort to create a faster, more efficient sail assembly.
The present inventor has met the challenge and designed a novel mast/boom assembly that overcomes or nearly eliminates the inefficiencies of the prior sail constructions. The assembly of the present invention departs from the conventional vertical mast system with a non-traditional mast assembly that essentially eliminates the turbulent wind shadow created by such vertical mast, as previously discussed, and replaces the conventional vertical mast with a "wire leading edge," i.e. an unimpeded edge along the leading edge of the sail. The entire sail is thereby allowed to enjoy an uninterrupted windstream which increases the efficiency and aerodynamic properties of the sail as a whole. In one embodiment, the mast of the present invention is in the shape of an "A"-frame with the sail appropriately supported between the "legs" of the "A" such that the sail's leading edge is unobstructed.
The present inventor has also devised an additional boom assembly that, among other things, increases the sail surface area through a modification of the sail shape. A separate "top" boom situated along the upper edge of the sail flattens the upper section of the sail and transforms it from a pointed configuration. Unlike the sail base that is fixed along its length, the sail top is usually fixed at only one point. Consequently, the sail top pressure difference with a pointed configuration does not generate lift, but rather, causes deflection of the sail trailing edge. This deflection tends to disturb the sail aerodynamics by disturbing or reducing the pressure differences about the sail, with a consequential net pressure difference and, therefore, a reduction in net "lift." The "top" boom of the invention effectively overcomes the deflection by creating a second sail edge that is fixed, similar to the base of the sail that is fixed along its length by the traditional or lower boom. Means are provided to attach the top boom to the mast assembly of the present invention in a controllable fashion, and further means are provided to control the movement of the top boom both independently and in conjunction with the lower boom.
The combination of the non-traditional mast assembly and "top boom" results in a superior sailing structure or configuration that overcomes the inefficiencies and deficiencies of the prior art. Coupled with the increased efficiency attributed to a wire leading edge, the "A"-frame embodiment with top boom configuration promises to be an improvement over all existing sail configurations in the area of lift generation. The ability to sail closer to the wind and generate greater lift or drive could prove to be the most significant advance since the advent of the winged keel.
3. Description of Related Art
The prior art evidences a continuing evolution in sail and mast design. The prior art does not, however, contemplate a mast assembly comprising the elements of the present invention. Some of the prior art references of note are as follows.
U.S. Pat. No. 2,364,578 issued to L. A. Wilkie on Dec. 5, 1944, entitled "Sailboat," discloses a wishbone-type double mast with an upper boom and without a lower, conventional boom. The upper boom of the Wilkie reference does not function in a manner similar to the present inventor's "top boom" since it does not support the tip of the sail. The Wilkie upper boom increases the wind-exposed surface area through a different wind exposure pattern across the face of sail. The deficiencies of the unsupported tip remain, however.
U.S. Pat. No. 3,827,386 issued to C. Faden on Aug. 6, 1974, entitled "Means for Lowering the Mast on Sailboats," discloses a slidable, collapsible mast. The sail assembly remains more or less conventional.
U.S. Pat. No. 4,044,702 issued to R. S. Jamieson on Aug. 30, 1977, entitled "High Efficiency Aerodynamic Sail System for Boats, and Method for Sailing," discloses a non-conventional tripod mast structure with a mast and swivel fitting for pivotal support of the sail head. Rotational support of the sail is accomplished without the use of a top boom or gaff or the like. The Jamieson sail does not operate on a wire leading edge like the assembly of the present invention.
U.S. Pat. No. 4,273,060 issued to I. Pavincic on Jun. 16, 1981, entitled "Sailing Vessel," discloses a non-traditional sailing system based on an omnidirectional hull arrangement. There is no mention of a collapsible mast or top boom assembly, but a double mast is shown.
U.S. Pat. No. 4,690,088 issued to F. Perini on Sep. 1, 1987, entitled "Sail Rigging with Fairing," discloses a small upper boom or peak situated near the mast head. Such peak function is well known in the prior art, and is not similar to that of the novel "top" boom of the present invention.
U.S. Pat. No. 4,886,008 issued to L. J. Puckett on Dec. 12, 1989, entitled "Frame Spar for Soft Airfoils," discloses a couple of different embodiments of an A-frame mast assembly. There is, however, no disclosure of a "top" boom assembly.
U.S. Pat. No. 4,940,008 issued to J. G. Hoyt on Jul. 10, 1990, entitled "Foldable Mast Assembly," discloses a foldable mast with a conventional mast leading edge. There is no mention of a "top" boom assembly.
U.S. Pat. No. 5,083,520 issued to C. Bonnet on Jan. 28, 1992, entitled "Mast, in Particular for Sailing Boat," discloses a vertical rockable plate located at the coupling of two masts at the mast heads designed to reduce the transference of any load, torque or twist to the mastheads from the rigging. Bonnet's plate is designed to alleviate rigging stresses upon the mast components.
U.S. Pat. No. 5,392,726 issued to T. A. Benze on Feb. 28, 1995, entitled "Sailboat" discloses a centrally swivelled lower or main boom within a dual mast assembly and Benze's continuation-in-part U.S. Pat. No. 5,423,274 issued on Jun. 13, 1995, discloses a swivel plate at the upper end of a similar dual stationary mast assembly. A rotatable sail boom capable of a 360.degree. rotation (two 180.degree. fore and aft rotations) allows the sail to accommodate changing wind patterns without requiring movement of the primary boom and mast assembly.
The prior art fails to disclose a non-traditional mast assembly with an upper and lower boom and an expanded sail area having a "wire" leading edge as opposed to a conventional, vertical mast leading edge. Furthermore, the prior art fails to disclose a mast/sail assembly with the ability to control the upper edge of the sail either independently or in conjunction with the lower edge of the sail. The "top boom" of the present invention operates within the framework of the present inventor's non-traditional mast to create an improved, highly efficient and proficient mast/sail structure with superior aerodynamic and control properties.